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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Bidentate ligands in gold chemistry : from stabilization of reactive species to catalysis
No full textCette thèse porte sur l'étude de complexes définis d'or, de la stabilisation de composés originaux à leur utilisation pour de nouvelles transformations. Une approche conjointe expérience/théorie a été employée. De nouveaux complexes d'or ont été synthétisés et caractérisés par différentes techniques spectroscopiques et de diffractométrie. Leurs réactivités, notamment dans des procédés catalytiques, ont été étudiées. Les calculs DFT ont aiguillé le choix des ligands/complexes d'intérêts. Ils ont permis d'analyser la structure électronique des nouvelles espèces isolées et d'élucider les mécanismes mis en jeu. Une vue d'ensemble de l'utilisation de ligands bidentes pour la chimie de l'or montrant leurs implications dans le développement de cette chimie est présenté dans le premier chapitre. Une comparaison des différents ligands bidentes accessibles rationnalise le choix de deux d'entre eux pour les études présentées par la suite. Le second chapitre concerne le développement de la réaction d'hétéroarylation des alcènes catalysée par le complexe MeDalPhosAuCl. Cette nouvelle transformation procède via un cycle catalytique Au^I/Au^III et combine addition oxydante et activation PI à l'or. Un mécanisme détaillé est proposé sur la base d'analyses RMN in situ, d'étude par marquage au deutérium et de calculs DFT. La réaction a pu être généralisée à un large panel de substrats et un changement inhabituel de régiosélectivité a été observé pour les alcènes internes cis ou trans. Le troisième chapitre est dédié à l'isolation et la caractérisation des premiers complexes d'or impliquant des liaisons hydrogènes Au···H-X. Grâce aux ligands hémilabiles (P,N), un contact proche entre l'or et l'hydrogène a été observé par DRX et la présence de la liaison hydrogène N-H···Au a été démontrée sans ambiguïté par spectroscopies RMN et IR. La nature de cette liaison a été méticuleusement analysée par calcul DFT fournissant des arguments en faveur d'une liaison hydrogène, interaction attractive non-covalente. Une étude in silico sur de nouveaux modèles, avec des interactions Au···H-X potentielles (X = N, O ou P, variations des ligands ou de l'encombrement stérique) a été réalisée pour donner des directives aux futurs travaux expérimentaux. Le quatrième chapitre porte sur l'étude de carbènes alpha-CF_3 d'or(I). L'intérêt est double : 1) très peu de carbènes alpha-CF_3 ont été isolés et caractérisés et 2) beaucoup de molécules bioactives ou de matériaux possèdent des substituants CF_3 augmentant l'intérêt pour les réactions de trifluorométhylation. Grâce au ligand bis-phosphine o-carborane, plusieurs carbènes alpha-CF_3 d'or(I) ont été synthétisés, isolés et complètement caractérisés par spectroscopie RMN multi nucléaire, DRX et spectrométrie de masse. La liaison M=C_carbène a été analysée par calculs DFT avec une attention particulière pour la description des orbitales moléculaires et la contribution relative donation/rétrodonation entre le fragment métallique et le carbène. La réactivité de ces nouveaux carbènes d'or vis-à-vis de réactions d'insertion et de cyclopropanation a été étudiée montrant que ces espèces imitent les carbènes alpha-CF_3 transitoires postulés pour d'autres métaux de transition.The present work deals with the study of defined gold complexes from the stabilization of original compounds to their use for novel transformations. A joint experimental/theoretical approach has been used. New gold complexes were synthesized and characterized by different spectroscopic means and diffractometry. Their reactivities notably in catalytic process were studied. DFT calculations guided for the choice of ligands/complexes of interest. They helped to analyze the electronic bonding of the new isolated species and to elucidate the involved mechanism. An overview of the use of bidentate ligand in gold chemistry showing their involvement in the expansion of this field is presented in the first chapter. A comparison of the different bidentate ligands available rationalize the choice of two of them for the following studies. The second chapter concerns the development of hetero-arylation reaction of alkenes catalyzed by the MeDalPhosAuCl complex. This new transformation proceeds via Au^I/Au^III catalytic cycle and merge oxidative addition and PI-activation at gold. A detail mechanism is suggested based on in situ NMR analyses, deuterium labelling studies and DFT calculations. The scope of the reaction has been explored for a large number of substrates and an unusual switch of regioselectivity was observed for internal alkenes cis or trans. The third chapter is dedicated to the isolation and characterization of the first gold complexes involving Au···H-X hydrogen bonding. Taking advantage of the hemilabile (P,N) ligands, a close contact between gold and hydrogen was observed by XRD and the presence of N-H···Au hydrogen bond was unambiguously demonstrated by NMR and IR spectroscopies. The nature of this bonding was thoroughly analyzed by DFT providing compelling evidence for noncovalent attractive hydrogen-type bonding. An in silico study on new models, with potential Au···H-X interaction (X = N, O or P, ligand and steric hindrance modulation) have been performed to provide guidelines for further synthetic work. The fourth chapter focused on the study of alpha-CF_3 gold(I) carbene complexes. The interest is twofold: 1) very few alpha-CF_3 carbene complexes have been isolated and characterized and 2) many bioactive molecules or materials bear CF_3 substituents, increasing the interest for trifluoromethylation reactions. Taking advantage of the o-carborane diphosphine ligand, several alpha-CF_3 gold carbene complexes were synthesized, isolated and fully characterized, at low temperature, by means of multinuclear NMR spectroscopy, XRD and mass spectrometry. The M=C_carbene bonding situation was analyzed carefully by DFT calculations with particular attention to the description of molecular orbitals and to the relative donation/retrodonation contribution between the metallic fragment and the carbene. The reactivity of this new gold carbene towards insertion reaction and cyclopropanation was studied showing that they mimic transient alpha-CF_3 metal carbene complexes
Ligands bidentes en chimie de l'or : de la stabilisation d'espèces réactives à la catalyse
Get PDFCette thèse porte sur l'étude de complexes définis d'or, de la stabilisation de composés originaux à leur utilisation pour de nouvelles transformations. Une approche conjointe expérience/théorie a été employée. De nouveaux complexes d'or ont été synthétisés et caractérisés par différentes techniques spectroscopiques et de diffractométrie. Leurs réactivités, notamment dans des procédés catalytiques, ont été étudiées. Les calculs DFT ont aiguillé le choix des ligands/complexes d'intérêts. Ils ont permis d'analyser la structure électronique des nouvelles espèces isolées et d'élucider les mécanismes mis en jeu. Une vue d'ensemble de l'utilisation de ligands bidentes pour la chimie de l'or montrant leurs implications dans le développement de cette chimie est présenté dans le premier chapitre. Une comparaison des différents ligands bidentes accessibles rationnalise le choix de deux d'entre eux pour les études présentées par la suite. Le second chapitre concerne le développement de la réaction d'hétéroarylation des alcènes catalysée par le complexe MeDalPhosAuCl. Cette nouvelle transformation procède via un cycle catalytique Au^I/Au^III et combine addition oxydante et activation PI à l'or. Un mécanisme détaillé est proposé sur la base d'analyses RMN in situ, d'étude par marquage au deutérium et de calculs DFT. La réaction a pu être généralisée à un large panel de substrats et un changement inhabituel de régiosélectivité a été observé pour les alcènes internes cis ou trans. Le troisième chapitre est dédié à l'isolation et la caractérisation des premiers complexes d'or impliquant des liaisons hydrogènes Au···H-X. Grâce aux ligands hémilabiles (P,N), un contact proche entre l'or et l'hydrogène a été observé par DRX et la présence de la liaison hydrogène N-H···Au a été démontrée sans ambiguïté par spectroscopies RMN et IR. La nature de cette liaison a été méticuleusement analysée par calcul DFT fournissant des arguments en faveur d'une liaison hydrogène, interaction attractive non-covalente. Une étude in silico sur de nouveaux modèles, avec des interactions Au···H-X potentielles (X = N, O ou P, variations des ligands ou de l'encombrement stérique) a été réalisée pour donner des directives aux futurs travaux expérimentaux. Le quatrième chapitre porte sur l'étude de carbènes alpha-CF_3 d'or(I). L'intérêt est double : 1) très peu de carbènes alpha-CF_3 ont été isolés et caractérisés et 2) beaucoup de molécules bioactives ou de matériaux possèdent des substituants CF_3 augmentant l'intérêt pour les réactions de trifluorométhylation. Grâce au ligand bis-phosphine o-carborane, plusieurs carbènes alpha-CF_3 d'or(I) ont été synthétisés, isolés et complètement caractérisés par spectroscopie RMN multi nucléaire, DRX et spectrométrie de masse. La liaison M=C_carbène a été analysée par calculs DFT avec une attention particulière pour la description des orbitales moléculaires et la contribution relative donation/rétrodonation entre le fragment métallique et le carbène. La réactivité de ces nouveaux carbènes d'or vis-à-vis de réactions d'insertion et de cyclopropanation a été étudiée montrant que ces espèces imitent les carbènes alpha-CF_3 transitoires postulés pour d'autres métaux de transition.The present work deals with the study of defined gold complexes from the stabilization of original compounds to their use for novel transformations. A joint experimental/theoretical approach has been used. New gold complexes were synthesized and characterized by different spectroscopic means and diffractometry. Their reactivities notably in catalytic process were studied. DFT calculations guided for the choice of ligands/complexes of interest. They helped to analyze the electronic bonding of the new isolated species and to elucidate the involved mechanism. An overview of the use of bidentate ligand in gold chemistry showing their involvement in the expansion of this field is presented in the first chapter. A comparison of the different bidentate ligands available rationalize the choice of two of them for the following studies. The second chapter concerns the development of hetero-arylation reaction of alkenes catalyzed by the MeDalPhosAuCl complex. This new transformation proceeds via Au^I/Au^III catalytic cycle and merge oxidative addition and PI-activation at gold. A detail mechanism is suggested based on in situ NMR analyses, deuterium labelling studies and DFT calculations. The scope of the reaction has been explored for a large number of substrates and an unusual switch of regioselectivity was observed for internal alkenes cis or trans. The third chapter is dedicated to the isolation and characterization of the first gold complexes involving Au···H-X hydrogen bonding. Taking advantage of the hemilabile (P,N) ligands, a close contact between gold and hydrogen was observed by XRD and the presence of N-H···Au hydrogen bond was unambiguously demonstrated by NMR and IR spectroscopies. The nature of this bonding was thoroughly analyzed by DFT providing compelling evidence for noncovalent attractive hydrogen-type bonding. An in silico study on new models, with potential Au···H-X interaction (X = N, O or P, ligand and steric hindrance modulation) have been performed to provide guidelines for further synthetic work. The fourth chapter focused on the study of alpha-CF_3 gold(I) carbene complexes. The interest is twofold: 1) very few alpha-CF_3 carbene complexes have been isolated and characterized and 2) many bioactive molecules or materials bear CF_3 substituents, increasing the interest for trifluoromethylation reactions. Taking advantage of the o-carborane diphosphine ligand, several alpha-CF_3 gold carbene complexes were synthesized, isolated and fully characterized, at low temperature, by means of multinuclear NMR spectroscopy, XRD and mass spectrometry. The M=C_carbene bonding situation was analyzed carefully by DFT calculations with particular attention to the description of molecular orbitals and to the relative donation/retrodonation contribution between the metallic fragment and the carbene. The reactivity of this new gold carbene towards insertion reaction and cyclopropanation was studied showing that they mimic transient alpha-CF_3 metal carbene complexes
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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